In mining placer gold in the riverbed, the use of a pan is a conventional practice. The pan is rolled from side to side, several times, in order to draw sand or gravel therein into a vortex. After removing the sand or gravel in the pan with the vortex flow of water, various minerals, namely placer gold, is left within the pan.
The conventional practice, however, required great skills to make the vortex flow, and was inefficient having a low productivity rate.